1. Field of the Invention
The present invention relates to a position detector such as a digital scale, an encoder, etc. applied to machine tools, industrial machines, precise length measuring machines or the like.
2. Description of the Related Art
A position detector which is a scale, a rotary encoder or the like is applied to machine tools such as milling machines, lathes, NC machine tools and the like, industrial machines, precise length measuring-angle measuring machines or the like. In the past, the position detector includes e.g. a thin plate-like scale member installed on a machine tool main body; a slider attached to a workpiece traveling table of the machine tool at a position opposite to the scale member; and a detection head attached to the slider. In addition, the position detector is used to read calibrations formed on the scale member for position detection and for controlling a processing-amount of the workpiece or the like.
Additionally, such a position detector is such that a carrier is provided on a slider-fixing section supporting the slider so that the slider is supported through the carrier and can be moved by the carrier.
Incidentally, in order to allow the position detector mentioned above to execute position detection with a high degree of accuracy and of resolution, e.g. a magnetic recording pitch (recording wavelength) of the scale members is reduced and a clearance between the detection head and the scale member is reduced. However, in the position detector, mechanical displacement occurs between the carrier and the scale member due to assembly accuracy, component tolerance or the like. This mechanical displacement varies the above-mentioned clearance and the like so that precise position detection cannot be executed, which leads to damage to the detection head in some cases. To solve such a problem, a position detector is proposed that is equipped between a carrier and a slider with an adjustable mechanism for suppressing displacement (see e.g. Japanese patent No. 3019685).
A scale device 100 shown in FIG. 9 is a traditional scale device and includes a carrier 102 supporting a slider 101; and a scale member 104 disposed to face a detection head 103 mounted on the slider 101. The detection head 103 and the scale member 104 are relatively moved and the detection head 103 detects a position signal from the scale member 104 for position detection. In addition, the scale device 100 includes an adjustable mechanism 107, at a position along the relative movement direction, composed of a carrier side coupling member 105 provided on the carrier 102 and a slider side coupling member 106 provided on the slider. This adjustable mechanism 107 suppresses the displacement between the detection head 103 and the scale member 104.
The adjustable mechanism 107 is provided in the scale device 100 so as to extend in the longitudinal direction of the scale device 104, in the relative movement direction. This configuration results from the scale device 100 having dimensional room in the longitudinal direction of the scale member 104. However, the configuration is not efficient in an applying direction of force for posture control with respect to reduction in the clearance between the scale member 104 and the detection head 103 and to retainment of such a reduced clearance.
A scale device 200 is also proposed in which a leaf spring 201 is provided in a plane vertical to a relative movement direction as shown in FIG. 10. Like reference numerals are given to the same functions and configurations of the scale device 200 as those of the scale device 100 and their explanations are omitted. The scale device 200 is such that one end of the leaf spring 201 is secured to a carrier 102 in a plane generally vertical to the longitudinal direction of a scale member 104. In addition, the other end of the leaf spring 201 is brought into contact with a plane opposite to a plane provided thereon with a detection head 103 of the slider 101. Thus, the slider 101 is biased toward the scale member 104.
However, in terms of the structure of the leaf spring, the scale device 200 having the leaf spring 201 is not such that the slider 101 is retained by a biasing force in a direction vertical to the scale member 104. As with the scale device 100 described above, the scale device 200 is inefficient and inaccuracy.
Also there is known a digital gauge which measures length through movement of a spindle. This digital gauge is generally used to measure a shape in a range as narrow as from 10 to 100 mm. In such a digital gauge having a narrow measuring range, the entire device is reduced in size. Thus, it may physically be impossible to maintain such a device-size and mount the adjustable mechanism 107 provided for the scale device 100.
The digital gauge described above needs assembly with a very high degree of mechanical accuracy, which poses a problem with costs.